If I knew ahead of time when and where I would have to use deadly force to defend myself then I would just avoid that place at that time. You can't know when or where so I carry any time I can.

As for statistics...here's my take. You can quote all sorts of percentages about chance of rain, chance of winning the lottery, chance of being attacked, but the true chances are only two. The chance is either 0% or 100% and you never know which it will be. If today is your 100% day and you are 0% prepared then I'm 100% sure you won't like the outcome.